The present invention relates to a disk control device for connecting a host computer with a disk device. More particularly, this invention relates to a command queue control device for controlling access for the disk device.
Formerly, in SCSI (Small Computer System Interface), Simple Queue Tag message, Ordered Queue Tag message, and Head of Queue Tag message are standardized. The Simple Queue Tag message is a message used in a disk device determining execution order in order to control the command queue. The Ordered Queue Tag message is a message for executing processing of the queue which is already subjected to queuing reservation. The Head of Queue Tag message is a message causing processing of queue to be executed under the highest priority. On the other hand, in open systems such as Windows, NT, UNIX, and so forth, only the Simple Queue Tag message is employed.
Now, there is a method for securing specific response in the disk device. For instance, the method for securing specific response in the disk device disclosed in the official report of Japanese Patent Application Laid-Open No. HEI 9-258907 is well known. In this official report, an external storage control device is provided with a predictive processing time generation means for predicting command processing time, a sending queue for storing queue so as to enter a sum of the predicted time within a period of a prescribed time interval, and a command batch generation means storing the command queue with already queuing reservation in a receiving queue into the sending queue when the sending queue becomes empty, the method for securing specific response is adopted such that command published to the disk device is limited.
In such the conventional technique, in the case of an open system such as a system employing the SCSI standard; Windows, NT, UNIX, and so forth, the disk device determines the execution order of the command according to a Simple Queue Tag message. Consequently, in order to secure specific response of the disk device, the open system always should limit publication of the command so as not to occur I/O-delay of the disk device.
In view of the foregoing, it is an object of the present invention, in order to overcome the above-described problem, to provide a command queue control device capable of securing specific response of the disk device simply.
According to a first aspect of the present invention, in order to achieve the above-described object, there is provided a command queue control device which comprises a reception queue storing means for storing therein a command received from a host computer, a means for allocating a tag of a queue management number to the command stored in the reception queue storing means, a means for adding a current time to a command queue to which the tag is allocated, an execution queue storing means for storing therein the command queue to which the tag and the current time are added, a means for publishing the command to a disk device while fetching the command queue stored in the execution queue storing means, a means for supervising a lapse time of the command queue stored in the execution queue storing means, and a means for implementing control so as to facilitate acceleration of command processing of the disk device when a command is detected by the supervisory means, which command is not executed in spite of a lapse of prescribed time period.
According to a second aspect, in the first aspect, there is provided a command queue control device, wherein the control means halts publication of a command to the disk device when a command is detected by the lapse time supervisory means, which command is not executed in spite of lapse of a second prescribed time period additionally after elapsing the previous prescribed time period.
According to a third aspect of the present invention, in the second aspect, there is provided a command queue control device, wherein the control means resumes publication of a command after completion of the whole processing of the command queues stored in the execution queue storing means.
According to a fourth aspect of the present invention, in the first aspect, there is provided a command queue control device, wherein the supervisory means calculates lapse time period of the command queue from difference between a time added to the command queue and a current time.
According to a fifth aspect of the present invention, there is provided a command queue control method comprising the stops of a step for storing a command received from a host computer in a reception queue storing means, a step for allocating a tag of a queue management number to the command stored in the reception queue storing means, a step for adding a current time to a command queue to which the tag is allocated, a step for storing the command queue to which the tag and the current time are added in an execution queue storing means, a step for publishing the command to a disk device while fetching the command queue stored in the execution queue storing means, a step for supervising a lapse time of the command queue stored in the execution queue storing means, and a step for implementing control so as to facilitate acceleration of command processing of the disk device when a command is detected by the supervisory means, which command is not executed in spite of a lapse of prescribed time period.
As described above, the command queue control device according to the present invention implements control of facilitating acceleration of the command processing of the disk device when the command which is not executed in spite of lapse of prescribed time period is detected, thus it is capable of facilitating command processing of the disk device even though delay occurs in the command processing of the disk device. Therefore, it becomes possible to secure specific response in the disk device.
The above and further objects and novel features of the invention will be more fully understood from the following detailed description when the same is read in connection with the accompanying drawings. It should be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention.